The flat was great, large living room, separate bedroom and awesome shower, much needed air con, good wifi, clean and tidy and 10-15mins walk to the sky train for easy access to the rest of Bangkok (the day porter will give you a lift on his moped if you ask nicely and you're feeling lazy and/or its really hot).
Pim was super helpful and accommodating. She made the experience easy even though she wasn't there to speak to in person, so have no fear about that.
Be aware that some of the roads quite close to the flat are on the red side of things (Sukhumvit 4 & 8), but this is Bangkok and Sukhumvit has lots to offer besides this... and it was Songkran whilst I was there, so the party scene was in full flow.
All in all I was very happy with the apartment, price and location, and wouldn't hesitate about staying here again.
Thanks for all your help Pim!